This invention relates to pneumatic radial ply tires and the interrelationship between the tire and its design rim.
Historically, with the introduction of the tubeless type tire, the design fitment of the bead portions of the tire to the design rim has increased in significance. This fitment insures that the tire remains air tightly sealed and securely fixed to the rim during vehicle use.
The typical rim has a bead seat and a rim flange that defines the contact zone with the tire bead. The tire bead has an annular surface between the bead heel and bead toe that upon assembly to the rim contacts the bead seat. The bead also has an annular surface radially outwardly of the bead heel, this annular surface contacts the rim flange when the tire is mounted and inflated on the rim.
The prior art teaches the use of a rim with cylindrical or very slightly conical bead seats. Typically such bead seats were inclined at an angle of 5.degree. relative to the axis of rotation of the tire. To ensure a proper fitment, the tire beads had an annular surface having a similar 5.degree. inclination relative to the axis of rotation, the beads having a slightly smaller diameter than the rim seat, thus upon assembly, a snug interference fit would be achieved.
As a later development, the radially innermost flexible toe portion of the tire between the toe and the annular tensile member comprised an inclined surface about 5.degree. greater than the rim seat. This added interference created by the angular variation facilitated sealing the tire.
The prior art tires had beads with a surface radially outwardly of the bead heel. This surface was designed to contact the rim flange, both the rim flange and this axially and radially outwardly surface being oriented at 90.degree. relative to the wheel axis. This area being under pressure while the tire is inflated contacts the rim flange essentially fastening the tire on the rim.
The prior art tires essentially relied on the rim seat and flange orientation to establish the shape and orientation of the bead, with the exception being the flexible toe portion of the bead.
It has been discovered that a tire made according to the present invention, having unique bead surfaces for contacting the rim can result in a tire having improved lower sidewall stiffness, better rolling resistance and improved comfort.